It is known that polyphosphate-based products are used for cleaning solid material in single-chamber spraying machines on account of the transparent film remaining behind on the workpieces and that phosphate/alkali metal borate-based products are used for cleaning workpieces of aluminum and its alloys. These cleaning products are generally marketed as powered mixtures and are delivered as such to a cleaning bath at intervals, the concentration of cleaning agent in the bath amounting to from about 0.1 to 20% by weight, dependent upon the particular application and the degree of soiling. If the cleaning solution is to be effective, the optimal concentration must be maintained. The optimal concentration may be determined by titration or by a conductivity measurement. The conductivity measurement for determining concentration may be carried out in conjunction with an automatic concentration adjustment.
One of the difficulties of using powdered products, particularly when they contain hydroscopic salts, is to ensure continuous uninterrupted introduction. In addition, it is precisely highly active, nonionic surfactants which are sensitive to solid caustic soda. During storage they change through oxidation to ether carboxylic acids, which impairs effectiveness with respect to certain greases and, in the case of degreasing sprays, causes troublesome foaming.
It is also known that liquid cleaning agents showing an alkaline reaction can be used for the purpose in question, having been obtained and regenerated by combining a strongly alkaline active-substance concentrate with a acidic active-substance concentrate. However, it has not been possible in this way, due to the poor solubility of boric acid and the inadequate stabililty of polyphosphoric acid, to produce products based on those acids. The use of agents containing orthophosphoric acid leads to a troublesome, white coating on the metal surfaces in the case of single-stage cleaning. Solutions of the type in question also effect aluminum.
Furthermore, it has also proven difficult to use highly concentrated active-substance components without an unnecessary concentration of hydrotropic substances and/or of potassium salts having a low active-substance content being required.